Short operas have practical advantages: they can be insubstantially enjoyable without staying around long enough to draw attention to their triviality; they can be intense without wearing you down; and you have a chance for an evening out and an early night on the same evening, or for a meal after the show. (Opera North's Eight Little Greats last season tried to market eight short operas on the basis that they weren't going to take too much out of your life, and they had some success.) But there are some subjects that actually need an hour or an hour and a quarter of music because that's the right amount: if done properly (by the composer, director and performers), they can be as satisfying as Götterdämmerung. One reason for this is that the fate of the universe is a fairly ridiculous topic for an evening's entertainment while a single human-scale idea, presented with sympathy and style, is quite likely to be worthwhile to most humans.

Almeida Opera's two conventional operas this year are both short, and both apparently aimed at children. Georges Asperghis' Little Red Riding Hood restored the pre-Angela Carter sexual message of the story in Asperghis' musically radical style. Richard Ayres' The Cricket Recovers, based on one of a series of children's stories by the Dutch author Toon Tellegen, was musically more conventional but charming and moving. The programme had a rather optimistic note that compared children's literature and opera as routes to fantasy and name-checked L'Enfant et les Sortilèges rather frequently. But Tellegen's world, somewhere between the bluff humour of Winnie the Pooh and the lachrymosity of Moomintroll, is straightforward in its values: there is pain and nastiness but creatures (or people) try to look after each other and there is lots of fun as well. The music is similarly straightforward, an evocation of the character of the animals, and of the weather in the wood where they all live.

The overture begins with depictions of the central characters – thumping Elephant and chirpy Cricket – and proceeds to a William Tell class storm that sweeps through the projected forest in stunning visual style in the Quay Brother's delightful setting. It all carries on from there in a sequence of short but thoroughly operatic scenes between various combinations of the beasties. The Cricket (Claire Wild, endearingly single-minded and trivial) wakes up and finds that she is less chirpy than usual; the Elephant (Jonathan Gunthorpe, very funny) keeps trying to climb trees, although he keeps falling painfully. Other animals try to help each of them: the Ant, heavy with memory, and with Anna Burford's clotted-cream contralto, knows what ails the Cricket but can't get through; the Owl (Burford again, a funny, scatty librarian with feathered bloomers) looks it up, but only alarms her with the certainty of its badness; the Vole (Allison Bell, an eager schoolgirl) tries to get the Elephant to climb a very small tree indeed, but he still falls; and the Sparrow, Simon Butteriss in personal trainer mode, tries to cure them both at once with energetic but ineffective mantras. The Cricket also has a distressing nighttime encounter with the horrific Gallworm (Keith Miller), who embodies and tips her over into violent despair; and the motherly Squirrel (Joanna Burton), although she doesn't really understand and frolics with all the others as summer arrives, sympathizes and helps drag out some of the gloom and set the Cricket on the path to recovery. Finally, the Elephant discovers that he can imagine climbing trees instead of doing it, and have all the fun with none of the bruises. Meanwhile, even the Sun finds the best way to shine.

While there was little to get really excited about in The Cricket Recovers, it certainly left a pleasant, warm feeling, and will be well worth reviving for children as well as adults. Stephen Sondheim and James' Goldman's Evening Primrose is probably at least as suitable for children, but mainly because most of them have a black sense of humour: warmth does not come into it. Previously performed once only, as a 45-minute television broadcast, and known only from the tape and from a recent recording of Sondheim's songs released together with the music from The Frogs, Evening Primrose is essentially a Twilight Zone episode with songs. A very poor poet, perhaps related to the one in Nahum Tate's Fairy Queen, goes to hide from the mockery of the world in a department store and finds that it is run out of hours by an even more cruel set of people who disguise themselves as mannequins when anybody else is around. It is in part a scary joke about department-store dummies moving around when you're not looking and in part a satire on the ossification of the establishment, a kind of sixties liberal inversion of Invasion of the Body Snatchers.

The music all belongs to the poet, Charles, originally played by Anthony Perkins, and Ella, a nineteen-year-old woman left in the store as a child by a mother immersed in spring dresses and kept as a servant by Mrs Monday, the evil old woman at the centre of the web. Charles, initially febrile and slightly deranged in his first song, "If you can find me I'm here", falls in love with Ella and becomes, if not noble, at least uplifted. Ella comes alive with Charles' love and starts to dream longingly of the outside world which she barely remembers ("I remember sky", a song whose deceptive simplicity hints that Sondheim, who wrote both the lyrics and music, was finally hitting his stride). They steal time together and talk to each other silently in the ingenious "When", in which the words and music of each of them are both in harmony and completely, painfully separate. They plan to escape in the lushly romantic "Take me to the world", which is reprised as they step outside the building. Sondheim provides emotional highs and occasional hope, if not spiritual uplift, against a background of grimy nastiness and social conformity in a way which foreshadows the much more substantial Company and Follies. It all works quite well.

Ian Marshall Fisher's production for Lost Musical involved many old chums, most of them apparently having a good time playing silent department-store dummies. Michael Matus as Charles resembled Robert Walker, Perkins' obvious role model, the comic-romantic lead of the movie of One Touch of Venus whose finest hour was the psychotic Bruno of Strangers on a Train. Matus has a not-bad music theatre voice and a fair way with words and was entertainingly frantic. Jennifer Higham was touchingly pale and gruel-fed as Ella. She clearly knows how to put a song over, but her lack of projection was worrying. Gary Raymond was splendidly sinister as Roscoe, the informal prime minister of the dummies. Betsy Blair was a touch too glamorous as the sinister, twisted Mrs Monday, but it was great to see her in action.

Mark Warman reconstructed the underscoring, directed the music from the piano, and, along with clarinetist Cristina Campuzano, provided atmospheric percussion effects.